Ireland will hold an historic referendum on liberalising its abortion law, considered one of the strictest laws in Europe. The referendum vote to repeal the ban in this traditionally Catholic country was predicted to win by a two-thirds majority.
An Irish Times poll of 4,000 said the "Yes" camp was leading by 68 percent to 32 percent. Another poll by national broadcaster RTE suggested an even bigger victory, with 69 percent to 30 percent backing reforms.
The abortion campaign had gathered steam after an Indian-origin woman died in 2012 after her requests to terminate a 17-week pregnancy were denied by the Catholic country. Savita Halappanavar has now become the face of the campaign in Ireland.
Ms Halappanavar, a 31-year-old Indian-origin dentist, had sought a pregnancy termination when told she was miscarrying, but the request was turned down due to Ireland's then strict anti-abortion laws. She died of blood poisoning days after miscarrying in October 2012.
The Irish Times survey suggested that women voted by 70 percent in favour of the proposal and 30 percent against. Support among men was 65 percent pro-choice and 35 percent anti-abortion.
"Thank you to everyone who voted today. Democracy in action. It's looking like we will make history tomorrow," Prime Minister Leo Varadkar, who backs the reform, said in a tweet.
People over 65, however, voted mostly against overhauling the current legislation, which only allows terminations in cases where the mother's life is in danger.
Among the youngest voters, 18-24-year-olds, the poll found that 87 percent of respondents voted to allow abortion.
The exit poll showed "an overwhelming desire for change that nobody has foreseen," wrote Irish Times deputy political editor Fiach Kelly.
"The victory for the 'Yes' campaign looks set to be neither narrow nor based on a few segments of Irish society. Rather, it will be carried high on the shoulders of a majority across the entire country," he said.
Kelly pointed out that in Connacht/Ulster, traditionally seen as the most conservative region in the country, the exit poll indicated that 59 percent voted for change.
He called it "the final casting off of old mores".
Nearly 3.5 million voters were asked whether they wanted to overturn the ban after an emotional and divisive campaign.
Results for different parts of the country are expected from 1100 GMT, with a final result to be announced later in the day at the main counting centre in Dublin Castle.
People arriving at polling stations from the early morning spoke about the momentousness of a complex decision that in many cases pitted moral against religious beliefs.
Ireland has traditionally been one of the most religious countries in Europe. However, the Roman Catholic Church's influence has waned in recent years following a series of child sex abuse scandals.
The referendum came three months before a visit by Pope Francis for the World Meeting of Families and three years after Ireland voted to legalise same-sex marriage despite the Church's opposition.
"The fact that it's illegal for somebody in Ireland to seek medical treatment, having to travel outside the country and to feel that guilt, shame and isolation, it's absolutely shocking," said Belinda Nugent, 43, a community activist voting in north Dublin.